This invention relates to a process for hydrolyzing urethane foam particles in a continuous manner to recover polyols and other chemicals. The invention is particularly applicable to the hydrolysis of polyurethanes such as polyether polyurethane from which liquid polyols can be recovered.
The low density and chemically resistant nature of scrap urethane foam has heretofore made it commercially unappealing to recover chemicals from it. Thus, scrap foam has generally been disposed of in land fills. It would be more desirable to recycle scrap foam if an economical and practical process and apparatus were available.
U.S. Pat. Nos. 4,025,559 to Johnson (filed Dec. 18, 1972; issued May 24, 1977) and 4,082,366 to Duff and Salloum (filed Mar. 18, 1977; issued Apr. 14, 1978), the latter assigned to the assignee of this invention, suggest the use of horizontally oriented reactors to hydrolyze scrap urethane foam. However, we have found that horizontal reactors are impractical for this application. In a paddle-type reactor, such as that shown in U.S. Pat. No. 4,082,366, the liquid polyol formed by the hydrolysis reaction contacts the unhydrolyzed foam particles and creates a slush. The slush is highly resistant to steam hydrolysis and the reaction proceeds too slowly to be practical. U.S. Pat. No. 4,025,559 relates to a horizontal reactor wherein the particles are transported through successive, screened, reaction zones by pneumatic means. The system requires an appreciable amount of energy just to maintain the particles in a fluidized state without plugging the screens. Moreover, the reactor is unsuited for processing urethane foams filled with any type of non-hydrolyzable particulate or thermo-plastic constituent. Such residue would quickly plug the reactor.
The use of open mesh baskets to retain urethane foam particles in contact with superheated steam is also known. However, this method, like those used to operate horizontal reactors, allows polyol from the hydrolysis reaction to soak into the remaining, unreacted, foam particles and retard their hydrolysis. Moreover, this is a batch rather than a continuous process.